1. Field of the Invention
The present invention generally relates to a black matrix substrate, a color filter using the substrate and a liquid crystal display device using the substrate. More particularly, it relates to a black matrix substrate which has a high dimensional accuracy and a good light-shielding property, a color filter which has a high contrast ratio, and a liquid crystal display device of excellent image quality.
2. Description of the Prior Art
Much attention has been paid recently to liquid crystal display device of monochromatic or full color type as a flat display device. In order to control three primary colors in such a liquid crystal display device, there are an active matrix method and a simple matrix method, each of which utilizes a color filter. The liquid crystal display device is constructed to perform color display by using picture elements of three primary colors (R, G, B) and controlling the transmission of each light of the three primary colors by electrical switching of the liquid crystal.
This color filter is constructed by forming each colored layer, a protection layer and a transparent electrode layer on a transparent substrate. In order to improve a color developing effect and a display contrast, there is formed a pattern (black matrix), which has a light-shielding property, at a boundary portion of each R, G, B picture element of the colored layer. In case of the liquid crystal display device of the active matrix method type, since a thin film transistor (TFT) is employed as a switching element, it becomes necessary to inhibit leaking of photo-current due to external light. Thus, it is necessary that the black matrix exhibit a very high light-shielding property.
As black matrixes used in the above mentioned prior arts, there are a black matrix obtained by forming a relief through photo-etching of a chrome thin film formed by vapor deposition or sputtering technique etc., a black matrix which is formed by dyeing a hydrophilic resin relief, a black matrix obtained by forming a relief using a photo-sensitive resin dispersed with black pigment, a black matrix obtained by. electrodeposition of a black electrocoating paint, a black matrix which is formed by printing technique, and so on.
However, in case of the above-mentioned black matrix, which is relief-formed by photo-etching the chrome thin film, although the accuracy in dimension is high because it uses the photo-process, the production cost is high because it requires the vacuum film forming process such as the vapor deposition or sputtering process and the production procedure is rather complicated. Further, in this case, in order to improve the display contrast under a strong external light circumstance, it becomes necessary to restrain the reflectance at the side of the observer, so that a low reflection chrome sputtering process etc. is required which further increases the production cost. On the other hand, in case of the above mentioned method of using the photo-sensitive resist dispersed with black color dye or pigment in advance, although the production cost can be lowered, the photo-process tends to be unstable because the photo-sensitive resist has black color. Consequently, a sufficient light-shielding property is difficult to obtain if more attention is paid to the accuracy in dimension. In this manner, there is a problem that a high quality black matrix is difficult to obtain. Further, in case of the above mentioned black matrix formation by use of the printing technique, although the production cost can be lowered to some extent, there arises a problem in case that the high dimensional accuracy is required.
On the other hand, the color filter is constructed by providing a colored layer, which consists of a plurality of colored patterns, between the space of the black pattern of the black matrix substrate, and by further providing a transparent electrode on this colored layer.
The liquid crystal display device is provided with the above mentioned color filter, an electrode substrate formed with an electrode on a substrate, and a liquid crystal layer, in which the transparent electrode of the color filter and the electrode of the electrode substrate are opposed to each other, and the liquid crystal layer is interposed between these electrodes.
However, in the above mentioned color filter and the liquid crystal display device, since the light-shielding property and the accuracy in dimension are not sufficient as aforementioned in the black matrix substrate used by them, it is often difficult to obtain a sufficient contrast ratio, and there is room for improving the image quality thereof.